1. Field
The disclosure of this application relates generally to medical devices and in particular to an articulated sheath applicable to remote robotic manipulation of surgical tools and instruments, such as endoscopes.
2. Related Art
Endoscopic surgical instruments and tools are well known and continue to gain acceptance in the medical field. An endoscopic instrument or tool generally includes a rigid or flexible tube commonly referred to as a sleeve or sheath. One or more channels extend along (typically inside) the sheath to allow access to end effectors located at a distal end of the sheath. Control mechanisms located at a proximal end of the sheath are configured to enable remote manipulation of the end effectors via the one or more channels. Accordingly, the mechanical structure of the sheath plays a key role in ensuring flexible access to end effectors, while protecting delicate organs and tissues of a patient. As used herein and elsewhere in the art of endoscopic medical devices, the term “end effector” refers to the actual working part of a surgical instrument or tool.
Endoscopic surgical tools may include clamps, graspers, scissors, staplers, needle holders, and other like tools, which serve to manipulate body parts (organs or tissue) during examination or surgery. Endoscopic instruments primarily include a light delivery system which serves to illuminate a body part under inspection, and an imaging system which serves to observe the body part under inspection. In a typical endoscopic light delivery system, the light source is located outside the patient's body and the light is delivered via an optical fiber system. In an endoscopic imaging system, an objective lens located at the distal end of the sheath transmits the image, formed by collected light, via a bundle of optical fibers to a viewing device or sensor located at the proximal end of the sheath. An example of a surgical endoscopic instrument includes a laparoscope, but many more exist.
Current endoscopic technology endeavors to reduce the amount of negative side effects and increase patient comfort, by providing minimally invasive surgery (MIS). However, one of the major shortcomings in the current state of the art of endoscopic tools is the lack of dexterity and sensitivity offered to health professionals (endoscopists and surgeons) who perform endoscopic procedures.
In particular, many conventional endoscopic instruments with rigid or flexible sheaths prevent the surgeon or endoscopist from easily maneuvering endoscopic tools and instruments due to the rigidity of the mechanical structure of the sheath. More importantly, rigid or flexible sheaths prevent the surgeon from obtaining an accurate feeling (feedback feeling) of the amount of pressure or force exerted by an end effector on the organ or tissue under inspection or operation.
For example, patent application publication US 2008/0287741 disclosed by Ostrovsky et al., describes an articulating mechanism for use in an endoscope or a catheter. The mechanism includes a series of stacked links disposed adjacent to one another and movable with respect to each other. Pull-wires provide tension and hold the staked links together while also allowing for controlled bending of the distal portion by movement of one or more of the pull-wires. Notably, the stacked links have no restoring force at the joint. The pulling of the wire will not distribute the bending forces evenly among the multiple links. The bending angles at each joint will be uneven at different joints. Thus, this sheath will not be controlled to a uniform curvature.
Another example, set forth in U.S. Pat. No. 7,785,252 to Danitz et al., discloses an articulating sheath for flexible instruments. The sheath having an elongated shaft with proximal and distal sections includes multiple pairs of links. The sheath also includes one or more sets of cables connecting the links of at least one discrete pair to another, such that movement of one link of the connected pair causes corresponding relative movement of the other link of the pair. Movement of the proximal section results in corresponding movement of the distal section. In this patent, flexible hinges receive compressive force by wire (cable) tension. To withstand the compressive force flexible hinges must be rigid in the axial direction, and the stiffness is designed to be large. This stiffness requires the wires tension to be large, which makes it difficult for the endoscopist or surgeon to obtain an appropriate feel of the amount of force being exerted by an end effector on the organ or tissue of a patient. In addition, when the mechanical structure of the sheath is controlled by a motor, it requires the motor to be large. For surgeries at the medical site, a large motor is a cause to hinder the precise and accurate maneuvers of surgeons, or becomes a cause of fatigue for the operator.
As used herein, the term “stiffness” refers to the rigidity of an object or material. Stiffness can be determined by the extent or amount to which an object or material resists deformation (e.g., bending, stretching or compression) in response to an applied force or tension. Stiffness may be considered as complementary or opposite to flexibility or pliability. That is, the more flexible an object or material is, the less stiff it is. In mathematical terms, the stiffness K of an object or material is a measure of its resistance to deformation in response to an applied force F. For an object having a single degree of freedom (e.g., one direction of bending) the stiffness is defined as K=F/δ, where δ is the displacement produced by the applied force. In the International System of Units, stiffness is measured in newtons per meter, while in English Units stiffness is measured in pounds (lbs) per inch. Although an object may be submitted to more than one deformation at a time (e.g., bending and stretching simultaneously), for the sake of simplicity, the discussions in the present application consider deformation of an object and its stiffness thereof in only one degree of freedom at a time.
Patent application publication US 2012/0078053 disclosed by Phee et al., discloses a Robotic system for Flexible Endoscopy. According to Phee et al., it is possible to implement a sheath having a fixed bending radius or a sheath having different bending radius each with the different length, so that an endoscope can be easily manipulated a gastrointestinal (GI) track to diagnose GI diseases.
In highly delicate surgical operations, such as neurosurgery, it is necessary to avoid the contact of endoscope or any other surgical tools with the critical brain tissues and nerves in the periphery of the lesion. To that end, it is necessary to maneuver with precisely controlled shape of the sheath and to know with a high degree of certainty how much force or tension is being applied to an end effector. It is also necessary to view in detail the lesion from various directions, often even from an opposite direction from which the endoscope is inserted. In this manner, the operation can be performed without damaging delicate structures located nearby the organ or tissue being operated. To that end, it is necessary to be able to easily bend the sheath to a controlled shape in all directions and in any location, without exerting excessive force.